1. Field of the Invention
The present invention relates to a thermal activation apparatus for a heat-sensitive adhesive sheet with a heat-sensitive adhesive agent layer formed on one side of a sheet-like substrate, the heat-sensitive adhesive agent layer being normally nonadhesive and becoming adhesive by being heated and thermally activated, a thermal activation method, a printer provided with the thermal activation apparatus, and a method of manufacturing an adhesive label which is the heat-sensitive adhesive sheet cut at a predetermined length.
2. Description of the Related Art
A heat-sensitive adhesive sheet as disclosed in JP 11-79152A has been conventionally commercialized, which has a heat-sensitive adhesive agent layer that becomes adhesive by being heated. Such a heat-sensitive adhesive sheet is advantageous in that the sheet before being heated is easy to handle, no industrial waste is generated since no release liner is required, and the like. In order to generate adhesion of the heat-sensitive adhesive agent layer of the heat-sensitive adhesive sheet, for example, the heat-sensitive adhesive agent layer is heated by a thermal head which is generally used as a printhead in a thermal printer. When the other side of the heat-sensitive adhesive sheet which is opposite to the heat-sensitive adhesive agent layer is a heat-sensitive printable layer, there is also an advantage that printing and thermal activation can be carried out by similar thermal heads.
A printer for printing desired letters, numerals, images, and the like on a printable layer of such a heat-sensitive adhesive sheet, cutting the heat-sensitive adhesive sheet at a predetermined length, and generating adhesion of the heat-sensitive adhesive agent layer to manufacture, for example, an adhesive label stuck to a product for indicating its price, name, or the like has been developed (see JP 2003-316265A, JP 3,329,246B and JP 2004-10710A). Such a printer includes a printing apparatus for recording desired letters, numerals, symbols, images, and the like on the printable layer and a thermal activation apparatus for thermally activating the heat-sensitive adhesive agent layer to generate adhesion thereof. The printer further includes a transport mechanism for transporting the heat-sensitive adhesive sheet and a cutter mechanism for cutting the heat-sensitive adhesive sheet at a predetermined length into labels. The printing apparatus is provided with a thermal head and the thermal activation apparatus is also provided with a thermal head. The thermal heads have substantially the same structure. Platen rollers for supporting and transporting the heat-sensitive adhesive sheet are disposed so as to be opposed to the thermal heads, respectively.
Generally, in a thermal activation apparatus, thermal energy applied to a heat-sensitive adhesive agent layer of a heat-sensitive adhesive sheet for generating adhesion of the heat-sensitive adhesive sheet is on the order of 1.5 to 2 times as much as the thermal energy necessary for making a printable layer colored in a printing apparatus. In addition, in the thermal activation apparatus, the whole thermal head (all the dots) is operated all the time in order to uniformly generate adhesion of the heat-sensitive adhesive sheet by heating the whole surface of the heat-sensitive adhesive sheet. As a result, the total thermal energy applied to the heat-sensitive adhesive agent layer in the thermal activation apparatus is on the order of 6 to 8 times as much as the total thermal energy applied to the printable layer in the printing apparatus, and thus, overheating within the thermal activation apparatus is a problem. In particular, when the thermal activation apparatus is continuously operated for a long time in order to manufacture many adhesive labels continuously, the thermal head for thermal activation itself becomes too hot and may be damaged by the heat. Thermal heads in recent years often have integrated circuits (ICs) mounted thereon. When the temperature becomes 90° C. or higher, even when the heating elements of the thermal head are not abnormal, there is a high possibility that a thermal breakdown of the IC is caused. When the thermal activation apparatus is continuously operated, the temperature of the thermal head for thermal activation reaches 100° C.-200° C., which may break the IC and make the IC unusable.
In recent years, since a printer is required to be smaller, a heat sink attached to the thermal head can not be so large, and the natural cooling is not expected to be so effective. Further, in order to miniaturize the printer, a wide space for dissipating heat can not be secured around the thermal head for thermal activation. Therefore, heat from the thermal head for thermal activation raises the temperature of the atmosphere in the narrow space around the thermal head for thermal activation, and not only the temperature of the thermal head for thermal activation but also that of other adjacent members is raised. For example, when an operation member which is manually swung is provided adjacent to the thermal head for thermal activation in order to maintain the thermal head for thermal activation and a platen roller for thermal activation within the thermal activation apparatus, the operation member also becomes hot, and a user operating the operation member feels it hot and, in some cases, may suffer a burn.
A thermal head for printing of the printing apparatus of the printer comes in contact with and heats the printable layer of the heat-sensitive adhesive sheet, while the thermal head for thermal activation of the thermal activation apparatus is structured to come in contact with and heat the heat-sensitive adhesive agent layer which is a side opposite to the printable layer. However, in the thermal activation apparatus, the platen roller for thermal activation inevitably partially comes in direct contact with the thermal head for thermal activation adjacent, to an edge of the heat-sensitive adhesive sheet which is cut into labels, which allows heat from the thermal head for thermal activation to be, directly transferred to the platen roller for thermal activation. Further, the platen roller for thermal activation may be heated via air around the thermal head for thermal activation. Therefore, the temperature of the platen roller for thermal activation is liable to be raised. As a result, when the thermal activation apparatus is continuously operated, the printable layer may be unintentionally colored by being heated not only by the heat transferred from the heat-sensitive adhesive agent layer of the heat-sensitive adhesive sheet heated by the thermal activation apparatus in the thickness direction to the printable layer, but also by the heat stored by the platen roller for thermal activation which comes in contact with the platen roller for thermal activation. The unintentional color may be a meaningless blur or may smudge or make unreadable a desired letter, numeral, image, or the like.
In addition, if the heat of the thermal head for thermal activation is dissipated inside the printer including the thermal activation apparatus, the heat may be transferred even to a roll of the heat-sensitive adhesive sheet before being transported to the thermal activation apparatus which is located outside the thermal activation apparatus, the heat-sensitive adhesive agent layer wound into the roll may be thermally activated, and the heat-sensitive adhesive sheet may stick to each other in the roll.